1. Field of the Invention
The present invention relates to a structure for attaching electronic components such as photointerrupters to attachment portions provided in various devices, and an image forming apparatus having such a structure.
2. Description of the Related Art
Various electronic components such as a photosensor for detecting a sheet passing a sheet conveyance path, a toner sensor for detecting the density and remaining amount of a developing agent, and an interlock switch for detecting the opening and closing of a manual insertion tray disposed at a side surface of an apparatus main body are mounted in an image forming apparatus such as a copier, a facsimile machine or a printer.
Generally, structures including screws are used to attach such electronic components in the apparatus main body of the above image forming apparatus. Specifically, screw holes are formed at specified positions of an attachment portion disposed in the apparatus main body, and through holes for the passage of the screws are formed in the electronic component. The screws fix the electronic component to the attachment portion by being screwed into the screw holes through the through holes.
However, such structures require many parts and many operation steps for the attachment of the electronic components, which leads to an increase in the production cost of the image forming apparatus.
An electronic component attaching structure designed to reduce the numbers of parts and operation steps is disclosed in Japanese Unexamined Patent Publication No. H09-319206. This structure includes an electronic component having a component-side locking claw and an attachment portion, to which this electronic component is attachable and which is formed with an apparatus-side locking claw or locking hole engageable with the component-side locking claw. The electronic component is fixed to the attachment portion by the engagement of the component-side locking claw and the apparatus-side locking claw or locking hole.
This structure is shown in detail in FIGS. 10 and 11. FIG. 10 shows an electronic component 100. This electronic component 100 includes a casing having the lower surface, and locking pieces 101 are integrally formed with the casing at the opposite ends of the lower surface with respect to longitudinal direction. These locking pieces 101 extend downward from the lower surface, and a locking claw 102 projects outward along the longitudinal direction of the casing from the leading end of each locking piece 101. On the other hand, FIG. 11 shows an attachment portion 110 to which the electronic component 100 is attached. This attachment portion 110 is in the form of a plate, and a rectangular locking hole 111 is formed to penetrate the attachment portion 110 in thickness direction. A dimension of the longer sides of this locking hole 111 is substantially equal to the longitudinal dimension of the electronic component 100, and a dimension of the shorter sides thereof is substantially equal to the width of the respective locking pieces 101 of the electronic component 100.
Both locking pieces 101 of the electronic component 100 are inserted into the locking hole 111. At an initial stage of the insertion, the locking claws 102 of the respective locking pieces 101 are pressed inward along the longitudinal direction of the locking hole 111 by the peripheral edges of the locking hole 111 of the attachment portion 110, and the respective locking pieces 101 are elastically deformed in the pressed directions. Upon completely passing the locking hole 111, the both locking claws 102 are restored to their initial positions by their elastic restoring forces. The respective locking claws 102 returned to the initial positions are engaged with the peripheral edges of the locking hole 111 of the attachment portion 110 as shown in FIG. 11, thereby preventing the electronic component 100 from being disengaged from the attachment portion 110.
This attaching structure can reduce the number of parts and operation steps since requiring no screws, whereby the production cost can be reduced.
However, in this structure, it is difficult to ensure sufficient rigidity for the respective locking pieces 101. Particularly in recent years, there has been a demand to reduce the costs of electronic components themselves to be mounted in image forming apparatuses, wherefore it is difficult to shape locking pieces integrally formed on casings of the electronic components in such a manner as to provide high rigidity, i.e. to be unlikely to deform.
This insufficient rigidity of the locking pieces 101 reduces reliability in fixing the electronic components. For example, if a pulling force acts on a wire connected with the electronic component 100 to exert a force of this direction to the electronic component 100 in the structure shown in FIG. 11, the both locking pieces 101 yield to this force to be deformed inward, whereby the both locking claws 102 are disengaged from the attachment portion 110, making it likely for the electronic component 100 to come off the attachment portion 110.